具有变量名称的命令行参数

Question

Generally when we have to access command line arguments in Java we use, args[] But this will be fine when command line input is like this,

//Demo is class
C:\java Demo 1 2

we can access 1 and 2 simply by using args[0] and args[1].

But I have encountered a situation where the command line input will be like this,

C:\java Demo --num1=12 --num2=14

If I have to get above values of num1 and num2, how do I get it?

I googled a couple of times for command line arguments with minor modification, every time I got the simpler version only.

I came across this answer here

How do I parse command line arguments in Java? .

But I am looking for a simple Java version with no third party libraries. Yes they make our life easy, but I want to learn Java way first.

public static void main(String[] args) {
    //simpler way to access command line arguments
    int first_num = Integer.parseInt(args[0]);
    int second_num = Integer.parseInt(args[1]);

    System.out.println("num1= "+first_num+", num2= "+second_num);

}

Not actually sure if by using

C:\ java Demo --num1=12 --num2=13

we will be able to directly access num1 and num2 in our main method or not.

But I need those values to be available in main method.

Hope I am clear, please let me know if any info needed.

Answer 1

To achieve what you want in a very simple manner you can try,

    public static void main(String[] args) {
    Map<String, String> argsMap = new LinkedHashMap<>();
    for (String arg: args) {
        String[] parts = arg.split("=");
        argsMap.put(parts[0], parts[1]);
    }

    argsMap.entrySet().forEach(arg-> {
        System.out.println(arg.getKey().replace("--", "") + "=" + arg.getValue());
    });
}

Note: There are more advance ways as per the duplicate post. But I guess you are looking for a very simple way.

Answer 2

I would suggest to have a look at Apache Commons CLI that is exactly made for your requirements:

http://commons.apache.org/proper/commons-cli/

Read the intro first: http://commons.apache.org/proper/commons-cli/introduction.html

It has a even a nice fluent API:

Options options = new Options();
options.addOption(OptionBuilder.withLongOpt("num1")
                               .withDescription("some info about the usage")
                               .hasArg()
                               .withArgName("VALUE")
                               .create() );